1. Field of the Invention
This invention relates to a method of manufacturing metallic materials with extremely fine crystal grains.
2. Description of the Prior Art
Although advances have been made in the development of metallic materials through heat treatment, plastic forming and the addition of alloy elements in order to control the microstructure of crystal grains 1 .mu.m or larger, the control of the mesoscopic structure, on the scale of 1 .mu.m or smaller, has stimulated the fields of semiconductor materials and chemical materials, and various research organizations have studied the methodology for control of mesoscopic structure and have obtained fundamental knowledge regarding materials design techniques. As a further extension of this, by developing basic technologies that can extend control of the mesoscopic structure of metallic materials to its limits, it would be possible to reduce our dependence on limited resources of alloy elements as much as possible, improve recyclability, and also dramatically improve the functionality of metallic materials as well as their strength and various other characteristics.
To explain this more specifically, one of the representative characteristics of a metallic material, the strength, is known to increase as the crystal grain size becomes finer according to the Hall-Petch relationship. In addition, characteristics (corrosion resistance, magnetism, etc.) that are made manifest by differences in the mesoscopic or nanocrystalline structure are also known to be different. On the other hand, current technologies for improving the performance of current metallic materials (addition of alloy elements, plastic forming, heat treatment, etc.) are approaching the limits to the degree by which the characteristics can be improved. Moreover, with current technologies it is difficult to obtain metallic materials with crystal grain sizes smaller than 1 .mu.m, and for this reason, the improvement of characteristics is heavily dependent on alloying or the use of composite materials, resulting in a loss of recyclability depending on the alloy composition of the metallic material, and moreover, the degree of dependence on limited resources of alloying elements increases.
To this end, by breaking down the crystal grain size 1 .mu.-m barrier or nearing this barrier, through the approach of increasing the fineness of the structure in the Hall-Petch region and improving characteristics (by mesoscopic structure control), we expect to establish fundamental technologies for materials development that are able to extend the strength, functionality and other aspects of the performance of the material to their ultimate limits, and thus control the structure of metallic materials up to their ultimate limits. Moreover, by developing such fundamental technologies, if the mesoscopic structure can be controlled on an extremely fine scale, not only can the strength, functionality and other characteristics of metallic materials be dramatically increased to near their theoretically predicted limits, but also we will be able to greatly reduce our dependence on the limited resources of alloy elements, and develop alternatives to and conserve rare resources (nickel, chrome, cobalt, copper, tin, zinc and other metals), and moreover, we can improve recyclability of metallic materials.
The fundamental object of the present invention is to implement mesoscopic structure control in order to improve the characteristics of materials by making the crystal grain size finer in accordance with the Hall-Petch relationship, as one technique for pursuing a process for making the crystal grain size finer that differs from the conventional technology.
In consideration of the demands that will be placed on future metallic materials with regard to improved durability, reliability, safety and the like, to be achieved through improvements in strength and functionality, a more specific object of the present invention is to provide a method for manufacturing metallic materials with extremely fine crystal grains in which mesoscopic structure control can be implemented by simple means in order to improve the characteristics of materials by making the grain size finer.